1. Field of the Invention
The present invention relates to a method and apparatus for controlling drives in a packaging machine which may simplify the driving mechanism of the packaging machine so as to reduce manufacturing steps and costs, and which may facilitate adjustments of speeds and other factors responsive to changes in articles to be packaged.
2. Description of the Prior Art
One type of machines in which the invention may be used is a machine of the so-called horizontal form-fill-seal class (hereinafter referred to as a horizontal packaging machine) in which a film of packaging material is supplied from a roll and drawn past a former which shapes the film into a continuous tube of packaging material, an article to be packaged is supplied through the former into the tube, and the tube is fed downstream, sealed to form a longitudinal tube seal on its two longitudinal edge portions, and ultimately sealed at package length intervals so as to form transverse seals and cut into individual packages. In such prior art horizontal packaging machines, different sections of the machine are driven by a single main motor. In this branch of the art, the heat seal formed longitudinally with respect to the direction of film advancement is referred to as the "center seal" and the seal formed transversely to the direction of film advancement is referred to as the "end seal", and these terms will be used herein and in the claims.
FIG. 1 is a schematic plan view of one typical driving system of the horizontal packaging machine and as may be seen, the driving system includes two drives which are powered by a single main motor 10. The first drive is a drive for an article infeed conveyor 12 and an end seal mechanism 14. Power is transmitted from the main motor 10 to a main shaft 16. The power is then transmitted through power transmission elements, such as chains and sprockets, to a drive shaft 18 for the article infeed conveyor 12 and a drive shaft 20 for the end seal mechanism 14, so that the respective mechanisms may be driven at the required speed. The second drive is a drive to feed a continuous film of packaging material (main plastic film), which drives a drive shaft 24 for a pair of rollers 22 for drawing the film from a supply roll, through power transmission elements such as timing belts and pulleys, to thereby feed the film of packaging material forward, and continuously form the same into a tube.
At this point, the speed of the article infeed conveyor 12 is so determined that the operation per pitch of an article pusher which serves to position the articles at predetermined intervals may be performed in timed relationship with each rotation of seal heads 26 in the end seal mechanism 14 (in the case that the rotary shaft has a single seal head). The rotation of the seal heads 26 has to be synchronized with the feed speed of the film of packaging material, at least while the seal heads are in contact with the tube of packaging material so as to seal (and cut) the same. To this end, a non-uniform mechanism 28 including an eccentric crank and other complicated elements is provided and is driven by a pilot motor 29 to regulate the speed of the seal heads 26.
Further, during the cutting operation by the end seal mechanism 14, the cutting locations have to be properly controlled so that they may depart from the pattern printed on the film of packaging material. To this end, the film of packaging material has register marks printed thereon which are sensed by a sensor. Thus, the sensed timing is compared with a value sensed by a photoelectric sensor 32 for a timing cam 30, to thereby control a pilot motor 36 for a speed-change pulley 34 and a pilot motor 40 for a differential gear mechanism 38. Additionally, the timing cam 30 is automatically set by a pilot motor 42.
It is to be noted that the main motor 10 also serves to drive a pair of rollers 44 for drawing the film of packaging material, another pair of rollers 46 for forming a center seal on the film and a discharge conveyor 48 for discharging the wrapped article.
Thus, the construction of known horizontal packaging machines is relatively complex in that power is transmitted from a common motor to many operating mechanisms, and the speed of each operating mechanism is varied by differential gear mechanisms and non-uniform speed mechanisms, and hence the machines require considerable labor and time to assemble. This may lead to malfunctions or operative difficulties with the machine. Also, the use of automatic regulating mechanisms in the form of pilot motors may lead to increased manufacturing costs.
Further, in the known horizontal packaging machines, it is necessary, when processing one article having a predetermined size which is different than a predetermined size of another article, to adjust the eccentricity of the crank in the non-uniform mechanism 28 for the end seal mechanism 14 so as to change the speed of the seal heads 26. However, it is mechanically difficult to make any substantial processing changes. For example, it is extremely difficult for a single motor to be employed so as to slowly feed a tube of packaging material in which a long article is wrapped and to effect end seals and cuttings on the tube. Additionally, the printed pattern registration has to be readjusted so as to be responsive to changes in the packaging materials and articles. Again, a substantial alteration is mechanically impossible.
European Patent Publication No. 83912 A1 discloses a packaging machine wherein the seal heads are driven by a first electric motor and the film of packaging material is driven by a second electric motor. However, the subject invention is directed to the specific arrangement wherein the first electric motor is dependent upon the second electric motor, and the machine of the publication is technically different from the present invention which will be hereinafter described.